Mechanical seal assemblies are conventionally used in fluid handling apparatus, such as pumps and the like, to substantially prevent the leakage of process fluid, which may be corrosive, along a shaft to the motor or bearing system which drives the apparatus. Such leakage could seriously affect the motor or bearing system and probably cause its destruction. Mechanical seal assemblies generally are constructed with a pair of seal rings, one connected to and rotatable with the shaft, and the other, non-rotatable and connected to the housing and the like. Each seal ring is provided with a lapped seal face, the seal faces of the rings oppose one another in engaging relationship, and rotate relative to one another. At least one of the seal rings is constructed of a relatively hard, non-weldable material, such as silicon carbide, tungsten carbide and the like, while the other seal ring is constructed of a similar or different material which could be silicon carbide, a graphitic material and the like. Means, such as springs, bellows and the like are employed to urge the seal faces in rubbing contact with one another. A slight leakage of fluid, which may be supplied to the seal faces, cools and lubricates the relatively rotating and engaging seal faces to prolong their useful operating life.
The rubbing contact between the seal faces of mechanical seals and the wear characteristics of seal rings dictates the use of relatively hard materials for the seal rings, such as the aforesaid silicon carbide and the like. The attachment and sealing of these hard materials to the supporting structure of the assembly is dependent upon the material used, the particular arrangement of components, and the operating conditions of the assembly. In some assemblies, a secondary elastomeric seal, such as an elastomer O-ring is used between the seal ring and its supporting structure, as for example, a support flange. In high temperature apparatus, on the order of 500 degrees F. and above, a secondary elastomeric seal between a seal ring and its supporting structure cannot be used because of the temperature limitations of the elastomeric material. Traditionally, high temperature mechanical seals have utilized lap joints or mechanical interference fits between the seal ring and its supporting structure constructed of low expansion alloy materials. The lap joint arrangement functions well, but is very maintenance intensive and critical due to dirt contamination during assembly. Lower expansion alloy seal ring supporting structure-seal ring interference fits are also, functional; however, because the lower expansion alloys characteristically have low corrosion resistance, they are not compatible with high temperature and corrosive fluids and fail rapidly, necessitating repair and/or replacement. The repair and/or replacement of a mechanical seal assembly is a costly procedure requiring considerable down time of the fluid handling apparatus with loss of productivity.